diff --git a/libraries/liblmdb/lmdb.h b/libraries/liblmdb/lmdb.h
index 4236218..803b286 100644
--- a/libraries/liblmdb/lmdb.h
+++ b/libraries/liblmdb/lmdb.h
@@ -226,6 +226,9 @@ typedef struct MDB_env MDB_env;
  */
 typedef struct MDB_txn MDB_txn;
 
+/** @brief Unique identifier for an active or recent transaction. */
+typedef size_t MDB_txnid_t;
+
 /** @brief A handle for an individual database in the DB environment. */
 typedef unsigned int	MDB_dbi;
 
@@ -448,7 +451,7 @@ typedef struct MDB_envinfo {
 	void	*me_mapaddr;			/**< Address of map, if fixed */
 	size_t	me_mapsize;				/**< Size of the data memory map */
 	size_t	me_last_pgno;			/**< ID of the last used page */
-	size_t	me_last_txnid;			/**< ID of the last committed transaction */
+	MDB_txnid_t  me_last_txnid;		/**< ID of the last committed transaction */
 	unsigned int me_maxreaders;		/**< max reader slots in the environment */
 	unsigned int me_numreaders;		/**< max reader slots used in the environment */
 } MDB_envinfo;
@@ -950,6 +953,19 @@ int  mdb_txn_begin(MDB_env *env, MDB_txn *parent, unsigned int flags, MDB_txn **
 	 */
 MDB_env *mdb_txn_env(MDB_txn *txn);
 
+	/** @brief Return the transaction's #MDB_txnid_t
+	 *
+	 * This returns the identifier associated with this transaction. For a
+	 * read-only transaction, this corresponds to the snapshot being read;
+	 * concurrent readers will frequently have the same transaction ID. For
+	 * a write transaction, this is always the snapshot read plus one. When
+	 * a write transaction aborts, the next transaction ID will be reused.
+	 *
+	 * @param[in] txn A transaction handle returned by #mdb_txn_begin()
+	 * @return A transaction ID, valid if input is an active transaction.
+	 */
+MDB_txnid_t mdb_txn_id(MDB_txn *txn);
+
 	/** @brief Commit all the operations of a transaction into the database.
 	 *
 	 * The transaction handle is freed. It and its cursors must not be used
diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index a4f13e6..87aa4f8 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -2775,6 +2775,13 @@ mdb_txn_env(MDB_txn *txn)
 	return txn->mt_env;
 }
 
+MDB_txnid_t
+mdb_txn_id(MDB_txn *txn)
+{
+    if(!txn) return (txnid_t)-1;
+    return txn->mt_txnid;
+}
+
 /** Export or close DBI handles opened in this txn. */
 static void
 mdb_dbis_update(MDB_txn *txn, int keep)